jamiswolf wrote:... Yes, I understand that this is a Respironics unit, but justbreathe was translating Resmed settings which is what I'm not familiar with. ...
My bad. I thought you had not realized it was a Respironics Unit. Sometimes the doctors use a prescribed settings that simply don't work for any specific machine, since a backup rate is something the Resmed machines do not do. (At least that I remember).
jamiswolf wrote:... I'm transitioning to a PR S1 BiPaP auto SV advanced soon...should arrive today. Too many central apneas and periodic breathing. So my interest is more then mere curiosity. ...
I thought I remembered that. Sorry to hear you need it. But I'm happy to say that most of us find our ASV machines to be very effective - once we get used to them. And the adjustment period can take a while. It seems to depend on how badly the central apneas were impacting you.
jamiswolf wrote:... So when functioning on the auto BiPap mode, it really only adjusts the EPAP upward to deal with OA? (always maintaining PSmin) Or is there an auto component to the IPAP as well? ...
Bingo! An auto-BiLevel machine only adjusts the EPAP to address the obstructive apneas. It does not adjust the Pressure Support that creates the IPAP value. So, if the EPAP has a minimum value of 8 and a maximum value of 12, and the Pressure Support is 4, then the current IPAP will be the value of the current EPAP plus 4.
But an ASV unit, adjusts the Pressure Support value to address central apneas. So, in addition to changing the EPAP value as needed, the machines keep an eye on the last 3 to 5 minutes of your breathing. I think the Resmed uses the last three minutes and the Respironics uses the last 5 minutes. At any rate, if the machine determines your breathing will not meet the moving average breath volume, then it will intervene and increase the pressure to increase the volume. Effectively, the machine adapts to the situation and becomes a ventilator. So, not only will the machine respond to a central apnea, it will also adapt as your breathing becomes too shallow (which often proceeds a central apnea). Due to this action, it is known as an Adaptive Servo-Ventilator (ASV) unit.
The basic theory is that central apneas tend to arise from several different factors.
The most common is due to cardiac problems. These problems seem to interfere (and/or damage) the normal chemo receptors that measure the CO2 buildup (indirectly) in the blood. The CO2 buildup normally triggers respiration. If the receptors are damaged, the buildup can increase to the point that breathing becomes shallower and shallower until a central apnea occurs. This is the undershoot side of the central apnea undershoot/overshoot cycle. After a while, the body rallies, resumes breathing and tends to trigger a bit of hyperventilation. This blows off the CO2. But unfortunately, it tends to overdo the situation. The hyperventilation tends to blow off too much CO2. This is of course the overshoot side of the undershoot/overshoot cycle. And since too much CO2 is expelled, the undershoot side of the cycles starts all over again. As you can imagine, this tends to cause the waxing and waning of the Cheyne-Stokes Respiration (CSR).
The second most common cause of central apneas is due to altitude. Essentially, as the air thins the O2 is not sufficient for some people to maintain proper respiration during sleep. Though this can be addressed by moving to a lower altitude, it can often be addressed via medication. And of course and ASV unit and/or supplemental oxygen are options.
The next most common cause of central apneas is an adverse response to the pressure of an xPAP device. Some people, in the presence of pressure some people seem to have impaired chemo receptors for the CO2 buildup. Of course, this is known as Complex Sleep Apnea Syndrome (ComplexSAS). To my knowledge, this process is not well understood at this time. However, it occurs in a significant percentage of patients who use xPAP therapy. In this instance, though older therapies included BiPAP S/T devices and/or supplemental oxygen, an ASV unit has been shown to be more effective.
A far more unlikely cause of central apneas is the use of opiates. Though this can occur within an addict of various opiates, it is more likely the optate is used to manage pain. Most doctors are VERY reluctant to take this route, due to the life threatening adverse reaction of suppression of the respiratory system. Essentially, the opiates interfere with the functioning of the brain stem, which helps regulate respiration.
The most uncommon cause of central apneas is due to a fault within the central nervous system. Typically this occurs due to some damage to the brain stem. This can either be caused by a neurological condition (these are often degenerative disorders that get worse over time) or due to trauma that resulted in damage to the brain stem, such as due to an automobile accident and/or an explosive device.
In most of these causes the Cheyne-Stokes Respiration pattern is generally not present. It tends to show up when cardiac problems (such as congestive heart failure) is present. But not always. Sometimes people just develop it without and cardiac problems.
Against all of these causes, the ASV units have proven to be an effective therapy. They tend to be most effective against standard central apneas and/or heart related issues. They tend to be least effective (and a bit trickier to tweak) against folks suffering from Complex Sleep Apnea Syndrome. The reason appears to be that the upper pressure must often be held in check to avoid adding to the problem. Thus, the respiration support of the ventilator mode is not as effective as it might be in other cases.
However, even folks with ComplexSAS find they can attain effective sleep therapy using an ASV unit. It just takes a little longer to get things tweaked.
jamiswolf wrote:... I'm certain I'll have more questions and it's reassuring to know friendly help is available. My Doc knows nothing about the machine and RT neither. Never set one up...small town. ...
No problem with a small town environment ... as long as they pull in the specialists when needed. I interviewed my sleep lab / DME when I went through my ASV titration. They laughed and told me that I could probably do the titration on myself, if I could be awake and asleep at the same time! Due to my neurological problems, I've had to learn a lot to try to get the most effective therapy possible.
jamiswolf wrote:... Justbreathe, best of luck with your new machine and thanks for undulgeing my little hijack on your thread. ...
I definitely agree with Jamis on this. Hope things go well. It was good to hear with the fixed EPAP you did better. It might take a few days/weeks for your AHI value to settle down. Essentially, I found that my body had to stop fighting the machine and work with it. But once that happens you may find a consistently lower AHI score (especially the apnea index).
Hope that long explanation helps.